Analog devices like transistors and diodes lead to opamps and analog computing. This takes more parts but with fast devices can be real time. Then came Logic and Digital Circuits, here also big systems will take too many parts. A very Old hp Logic Analyzer instrument, could be HP1607A, had more than five large PCBs, Toggle Switches and numerous 74Fxx TTL Chips. I tried to revive it, it could not be fully restored.
Embedded Microcontroller - delabs
Then came the solution the Microprocessor. Here the entire system goes into the firmware and a Hardware Tool Set in the Microprocessor made up of Logic and Math is sequentially used to perform the same operation that would require innumerable Gates in a plain hardware digital circuit. But as it performs the operations one after another, it takes time and is defined by the CPU Clock Speed.
When the External RAM and EPROM and other peripheral devices moved into the main package, MicroController were born. When more external devices merged with the MicroController. It formed a nearly complete computer, this is known as the SOC.
There are two things to learn, build something to completely learn a concept. This is a tough but thorough way of
learning. The easier way is to learn from examples. Hacking and Reverse Engineering also good for students to digest methods exhaustively.
This way leads to things like innovation/improvement and inventions. That is A Better way
I had once serviced a DMM decades ago. It had something like a custom 8039. This was decades back. It was a 5-1/2 or more. It had a Watchdog built with CMOS 40xx chips. I never understood watchdogs then, they were not even called watchdogs.
The "Tick" is the heartbeat of a RTOS, not only it keeps polling all peripheral chips or I/O, It cannot skip a beat, even high priority interrupts cannot stop the routine tasks or even delay them. If it has to sample a Analog level ten times a second and produce a output control byte at the same speed; It could be RTOS for Process Control. For a rocket this will not be RTOS. Speed and not missing a step. Many times faster than the process it is meant for, probably ?